This invention relates in general to diaphragms for microphones and in particular to a diaphragm for electrostatic and electrodynamic microphones which have a distinct directional pattern.
German Pat. No. 452,961 discloses a so-called resonance-free diaphragm designed as a unstretched or non-taut skin of rubber or the like, to which carbon grains of various size are fixed by an adhesive. The indicated thickness of the rubber skin is 0.1 mm. Such a diaphragm is usable only for carbon microphones. German OS No. 30 11 056 deals with a molding material allegedly suitable also for diaphragms of electroacoustic transducers. More particularly, this prior art molding material is a mixture of plastics to which acrylnitrile-butadiene rubber (about 20% of the total mass) may be admixed. Since even pickup arms, housings, etc. may be formed from this material, no elastic diaphragm material is concerned. It is therefore impossible in practice to make electrostatic or electrodynamic microphones of the above-mentioned kind with the above prior art diaphragms. In German Pat. No. 452,961, the diaphragm is usable only in carbon microphones while in the other reference, the molding material is suitable only for loudspeaker diaphragms.